Recent federal initiatives, such as Race to the Top, School Improvement Grants, and Teacher Incentive Fund grants, aim to ensure equal access to effective teaching for disadvantaged and non-disadvantaged students. Four papers examine the extent to which there is a gap between these two groups in the effectiveness of their teachers. To measure teacher effectiveness, each paper uses value added, a statistical measure of teacher effectiveness that attempts to isolate a teacher’s contribution to student achievement. The first paper lays out a theoretical framework for understanding how measures of a teacher's value added can influence the measured relationship between teacher effectiveness and student disadvantage. The authors assume that a policy intervention changes the distribution of teacher effectiveness, and use simulation techniques to examine how various popular estimators of teacher value-added perform in measuring the correlation between teacher effectiveness and student disadvantage. The second paper applies a value-added model to data from 2000-2001 to 2004-2005 from Florida and North Carolina to compare the effectiveness of teachers in schools serving primarily students from low-income families with teachers in schools serving more advantaged students. The results show that the average effectiveness of teachers in high poverty schools is lower than teachers in other schools, and there is significantly greater variation in teacher quality among high poverty schools. These differences are largely driven by less productive teachers at the bottom of the teacher effectiveness distribution in high-poverty schools. The findings suggest that measures that induce highly effective teachers to move to high-poverty schools and which promote an environment in which teachers’ skills will improve over time are more likely to be successful. The third paper describes the prevalence of highest-performing teachers in ten purposely selected districts across seven states. The overall patterns indicate that low-income students have unequal access, on average, to the district’s highest-performing teachers at the middle school level but not at the elementary level. However, there is evidence of variation in the distribution of highest-performing teachers within and among the ten districts studied. Some have an under-representation of the highest-performing teachers in high-poverty elementary and middle schools. Others have such under-representation only at the middle school level, and one district has a disproportionate share of the district’s highest-performing teachers in its high-poverty elementary schools. The final paper examines the distribution of teacher effectiveness in the District of Columbia (DC) by measuring the teacher effectiveness gap, the average difference in teaching effectiveness faced by students eligible for a free or reduced-price lunch compared to ineligible students. One of the unique features of the DC school system is its reliance on a great variety of charter schools, which educate over forty percent of the students. The overall gap is decomposed into (1) gaps that arise between the DC public schools and various charter school local education agencies, resulting from the distribution of teachers across LEAs in the local labor market for teachers, and (2) gaps that arise within LEAs, resulting from LEA- and school-level assignment policies of teachers to students.